Webs of homofilament crimped thermoplastic fibers are useful for various fluid handling or retaining materials and the like because of their open structure, resiliency, and economy of manufacture. Particularly, the use of a single thermoplastic polymer in the making of the crimped fibers is good for economical and consistent manufacture. However, one may lose the benefit of the lofty crimped fiber web structure if the homofilament crimped web is processed by known means. Because a homofilament crimped web is usually loosely bonded, such means will include compaction of the web or exposure to high heat, in order to increase the integrity of the web for later processing. Compaction, as in Jacobs et al., U.S. Pat. No. 5,810,954, will decrease bulk or loft of the web through mechanical action as the web is drawn between compaction rollers. Also, this type of processing may result in mechanical failure of the rollers as the filaments become entangled in the mechanical works of the rollers.
In another known means of increasing web integrity, exposure to high heat in an effort to provide thermal bonding between filaments of the web, as in the hot air knife (HAK) teaching of U.S. Pat. No. 5,707,468 to Arnold et al., will result in relaxation of the fiber crimp with resultant loss of bulk for the web.
Conversely, it has been found that the crimps of a homofilament crimped thermoplastic fiber web may be crystallized, or set, to retain their loft through low applications of heat as in U.S. Pat. No. 6,123,886 to Slack. However this treatment does little to increase the integrity of the web for modem, high-speed, line-transfer manufacturing, and as taught in Slack, is a slow, off-line process unsuitable for economical manufacture rates.
Therefore, there is a need in the art for methods and materials utilizing the lofty crimped homofilament nonwoven web with high loft intact and with sufficient integrity to the lofty crimped web to enable high speed manufacturing processes to achieve economy.